1. Field of the Invention
This invention relates to an ion modulating electrode used as a recording unit in an electrostatic recording method.
2. Description of the Prior Art
Among electrostatic recording methods, a method employing multi-stylus electrodes has been mainly utilized but there is a limit to the quality of an image formed by this method. In an electrostatic recording method employing an ion modulating electrode, charged ink mist is passed through said electrode to form a visible image directly on a recording member. In order to increase the recording speed in the present method, it is necessary to increase the area of the apertures through which the ion flows, by which, however excessive dispersion of the ink mist adversely affects the quality of the image.
The construction and operation of a screen for modulating of an ion flow, an improvement which is provided by the present invention, will be described with reference to FIG. 1. Referring to the drawing, reference numeral 1 denotes an ion generator having a corona wire 12 generally a tungsten wire 40-100 .mu.m in diameter, in an earth plate 11.
Reference numeral 2 denotes an ion modulating electrode showing an example of the construction thereof, in which a first conductive layer of a conductive material 21 and a second conductive layer of a conductive material 22 are separated from each other by an insulating layer 23 with apertures 24 formed just under the corona wire 12. Each of the conductive layers 21, 22 generally comprises a conductive metal, such as copper or aluminum. The insulating layer 23 may consist of an air layer, or an insulating polymer film, such as a polyimide film or a polyester film. In order to apply an ion flow effectively to an electrostatic recording member 3, it is preferable that the conductive layers 21, 22 and insulating layer 23 be thin, specifically, the conductive layers should have thicknesses of not more than 100 .mu.m and the insulating layer should have not more than 200 .mu.m.
The electrostatic recording member 3 comprises a dielectric layer 31 and a backing electrode consists of a conductive layer 32. A high positive voltage is applied between the corona wire 12 and the backing electrode 32 of the electrostatic recording member 3 from a high voltage power source 13. The ion modulating electrode 2 is disposed between the ion generator 1 and the electrostatic recording member 3. The first conductive layer 21 of the electrode 2 is positioned on the side of the ion generator 1 and has a DC bias potential applied to it by a DC power source 25. An ion modulating signal 26 is applied to the second conductive layer 22 to form ion modulating fields in the apertures 24 via an electric field due to a potential difference between the conductive layers 22 and 21, and thereby controlling the passage of the ion flow from the ion generator 1 toward the electrostatic recording member 3. For the above operation, at least one of the conductive layers 21 and 22 need to be segmented.
In order to effectively pass an ion current to the electrostatic recording member 3 through the screen 2, the voltages of the DC power source 25 and voltage signal 26 are maintained for higher than that of the conductive layer 32 of the electrostatic recording member 3, usually by 500-3000 V.
The ion modulating electrode 2 is provided with a row, or a plurality of rows, of electrically separated apertures 24. Ion flow through the apertures 24 to form an electrostatic latent image on the electrostatic recording member 3. The resolution of the electrostatic latent image is determined in accordance with the diameter and pitch of the apertures 24. The apertures 24 are formed by means of laser beams, or by chemical etching. It is said that the density and opening rate of the apertures 24 are preferably 50-500 mesh and not less than 30%, respectively.
Operations for blocking and enhancing the passage of the ion flow will be described.
In an aperture of the electrode 2, a potential of the second conductive layer 22 is kept lower than the potential of the conductive layer 21. Accordingly, an ion enhancing field is produced in the aperture 24 from the first conductive layer 21 to the second conductive layer 22. As a result, the passage of positive ions, which are produced by the ion generator 1, through the mentioned aperture is enhanced, so that the ions reach the surface of the electrostatic recording member 3. In another aperture in the electrode 2, a potential of the second conductive layer 22 is kept higher than the potential of the conductive layer 21. Accordingly, an ion blocking field is produced in said another aperture from the second conductive layer 22 to the first conductive layer 21. As a result, the passage of the positive ions produced by the ion generator 1 through said another aperture is blocked. Thus, electrostatic latent images are formed on the dielectric layer 31. These electrostatic latent images are developed, fixed and visualized by ordinary methods.
In order to effectively direct the ion flow onto the electrostatic recording member 3 it is preferable that distances d.sub.1, between the corona wire 12 and the electrode 2, and d.sub.2, between the electrode 2 and electrostatic recording member 3, be small. Distance d.sub.1 is usually not more than 20 mm, and d.sub.2 not more than 5 mm.
In an electrostatic recording method using an ion modulating electrode, the corona wire 12 is disposed close as possible apertures 24 to maximize the recording speed. However, when a corona wire 12 is disposed too close to apertures 24 in a conventional ion modulating electrode, a sparking phenomenon occurs between the corona wire 12 and conductive layer 21, breaking the ion modulating electrode. Therefore, the corona wire 12 cannot be disposed close to the apertures 24, thus limiting the recording speed.